If the youth have the guns, let them keep these guns so that if we call them to come... [they can] confront what is coming from the northSalva Kiir, South Sudan's president

He said if Southern troops don't comply than Khartoum will "chase them out" and "hit deep inside South Sudan".

He dismissed the Council's demand that Sudan also end aerial bombardments, saying reports of such attacks were fiction.

South Sudan's UN ambassador Agnes Oswaha supported the idea of talks, but said outstanding issues needed to be resolved immediately.

She added that South Sudan would only withdraw from Heglig if an international force was deployed to the area.

Earlier the President of South Sudan, Salva Kiir, told his parliament that he will not withdraw his troops.

He urged MPs to mobilise their supporters and prepare for war should Khartoum refuse to talks.

Meanwhile, South Sudan's army spokesman told the BBC Sudanese aircraft had bombed two towns, killing one person.

The fighting along the oil-rich border region is the worst since South Sudan gained independence last July.

Speaking in Geneva earlier, UN Secretary General Ban Ki-moon said he was gravely concerned about the situation and urged both governments to "cease hostilities immediately" and hold a presidential summit to negotiate a solution.

On Wednesday, Sudan admitted that South Sudan had seized the town of Heglig, which is home to facilities that account for around half of Sudan's oil production.

War songs

Oil dispute

South Sudan took most of the oil fields when it seceded from Sudan last July

But it has to export its oil using pipelines through ports in Sudan's territory

South Sudan depends on oil sales for 98% of its revenue; transit fees account for 36% of Sudan's budget

South Sudan stopped pumping oil in January in a row over transit fees, accusing Sudan of stealing oil worth $815m (£518m)

Until 8 April, Heglig was firmly in Sudan's control, and the oilfield provided more than half of Sudan's oil

South Sudan accuses Sudan of using Heglig to launch attacks on its oil installations

The area is internationally recognised as Sudanese territory, but South Sudan disputes this.

South Sudan says it took Heglig in order to prevent the Sudanese army organising attacks from there.

In response, Sudan ordered a general military mobilisation and has vowed to act with "all means" against the attack. It has also pulled out of African Union-led negotiations with South Sudan.

In parliament in South Sudan's capital, Juba, on Thursday, Mr Kiir said he told Mr Ban: "I'm not under your command" and that although he did not want war with Khartoum, his country had to act in self-defence.

"I always say we will not take the people of South Sudan back to war, but if we are being aggressed [attacked] like this we will have to defend ourselves," he said.

The president, a former rebel commander, said that MPs, who are returning to their consistencies for a parliamentary recess, must mobilise all their "people" and tell them to forget "tribal conflicts" and unite to confront a more pressing danger.

The BBC's Nyambura Wambugu in Juba said parliamentarians responded with cheers, the chanting of the ruling party slogans and war songs used during the two-decade civil war.

MPs do not necessarily want war but were happy that the president reflected the anger many in South Sudan feel about the months of Sudanese bombardments, she says.

'Aerial bombardment'

The border clashes have been going on for weeks - the most serious since South Sudan's independence

In Khartoum, Sudan's leader Omar al-Bashir said war was "not in the interests of either South Sudan or Sudan".

"Our brothers in South Sudan have chosen the path of war, implementing plans dictated by foreign parties who supported them during the civil war," AFP news agency quotes him as saying.

Earlier in the day, Sudanese aircraft dropped five bombs on a bridge linking Bentiu and neighbouring Rubkotna, in Unity state, leaving at least one person dead and four injured, according to South Sudan officials.

"This is an indiscriminate bombing by Sudan's armed forces that has been conducted for almost one year now. They are bombing innocent civilians in northern parts of Unity state," army spokesman Col Philip Aguer told the BBC.

Correspondents say Sudan, having lost most of its oil when the south seceded, will not tolerate losing any more.